Did You Know!
Humans Have a “Spleen Reflex” for Underwater Survival
In people, especially elite freedivers, holding your breath underwater triggers the “spleen contraction reflex,” which boosts oxygen supply. The spleen squeezes out red blood cells rich in oxygen, temporarily increasing blood oxygen capacity—essentially giving you a natural “blood doping” effect. This is part of the mammalian dive reflex, an ancient adaptation for survival underwater.
